1. Field of The Invention
The present invention relates generally to an improvement on the buckle used on the seat belts in an automotive vehicle or the like, and more particularly to a buckle for a seat belt in which a false locking prevention system is provided in order to lock the seat belt completely.
2. Description of The Prior Art
As is well known, there are various structures of the seat belt buckle fixing one end of the seat belt. A typical conventional structure of seat-belt buckle is disclosed in Tokkai-Sho No. 50-109037 (Japanese Patent Application Open to Public Inspection No. 109037/1975). In such a conventional buckle, a tongue connected to one end of the seat belt is locked by a latch. Since the latch is always urged upwards by a latch spring, when the tongue is not completely inserted or is slowly inserted into the buckle, it is also urged upwards by the latch spring so that it may be not completely engaged with the latch but may be held tightly between the upper surface of the latch and the inner surface of the buckle casing. Thus, the seat-belt user is apt to assume that this unlocked condition is the perfectly locked state; that is, this condition is often called "false locking". When the vehicle is suddenly decelerated in an emergency such as a collision, the tongue easily slips out of the buckle if the user has not been aware of "false locking". Accordingly, such false locking state not only reduces the effect of a seat belt in an emergency, but can also cause serious accidents.
In the prior art, the conventional buckle is further provided with an electrical circuit indicating that the buckle is locked. However, it requires some variety of display device, thereby increasing the cost of the buckle.